Finnish researchers found that haemoglobin levels that are within the normal range but at the lower end may be beneficial for health, particularly for glucose metabolism and cardiovascular health.

Haemoglobin is a vital protein found in red blood cells and its primary function is to transport oxygen from the lungs to various tissues throughout the body. According to Finnish reference values, normal haemoglobin levels are 117–155 g/l for women and 134–167 g/l for men.

“The normal range is therefore quite broad, and previous studies have suggested that a haemoglobin level within the normal reference values but at the lower end of the range may be beneficial to health,” says Postdoctoral Researcher Jooa Norha from the University of Turku in Finland.

Health benefits linked to glucose metabolism, physical fitness, and heart and liver health

In a new study, the researchers measured the haemoglobin levels of 64 adults and conducted a comprehensive assessment of their metabolism and cardiovascular health.

“We found that lower haemoglobin levels were particularly associated with better glucose metabolism, but also with physical fitness, cardiovascular health, and reduced liver fat,” Norha explains.

Although the number of participants was limited, the researchers note that the study's reliability is increased by its follow-up design and the rigorous imaging and laboratory tests conducted on the participants.

“We measured glucose metabolism, i.e. insulin sensitivity, by administering insulin and sugar directly into the participants’ bloodstream in a laboratory setting. This allowed us to study how the body reacts to insulin,” Norha elaborates.

Low haemoglobin level associated with lower mortality rate

Previous studies have yielded similar findings, as lower haemoglobin levels have been associated with lower overall mortality and cardiovascular mortality in Finnish data.

“The mechanisms behind the impact we have observed are not entirely clear. It has been suggested that lower haemoglobin levels — while still within the healthy range — trigger cellular protective mechanisms related to oxygen deprivation, which promote cellular metabolism,” explains the study’s Principal Investigator Ilkka Heinonen.

However, the researchers do not recommend measuring haemoglobin unnecessarily in asymptomatic and generally healthy people. Abnormally low or high values should be discussed with a physician.

The study was conducted at the Turku PET Centre in collaboration with the University of Turku, Turku University Hospital, Åbo Akademi University, and the UKK Institute.